1) Field of the Invention
The present invention relates to an axial multi-piston type compressor for an air-conditioning system used in a vehicle such as an automobile.
2) Description of the Related Art
A swash plate type compressor is well known as representative of an axial Multi-piston type compressor, and comprises: front and rear cylinder blocks axially combined to form a swash plate chamber therebetween, the combined cylinder blocks each having the same number of cylinder bores radially formed therein and arranged with respect to the central axis thereof, the cylinder bores of the front cylinder block being aligned and registered with the cylinder bores of the rear cylinder block, respectively, with the swash plate chamber intervening therebetween; double-headed pistons slidably received in the pairs of aligned cylinder bores, respectively; front and rear housings fixed to front and rear end faces of the combined cylinder blocks through the intermediary of front and rear valve plate assemblies, respectively, the front and rear housings each forming a suction chamber and a discharge chamber together with the corresponding one of the front and rear valve plate assemblies; a rotatable shaft member arranged so as to be axially extended through the front housing and the combined cylinder blocks; and a swash plate member securely mounted on the shaft member within the swash plate chamber and engaging with the double-headed pistons to cause these pistons to be reciprocated in the pairs of aligned cylinder bores, respectively, by the rotation of the swash plate member.
The front and rear valve plate assemblies have substantially the same construction, in that each comprises: a disc-like member having sets of a suction port and a discharge port each set being able to communicate with the corresponding one of the cylinder bores of the front or rear cylinder block; an inner valve sheet attached to the inner side surface of the disc-like member and having suction reed valve elements formed integrally therein, each of which is arranged so as to open and close the corresponding suction port of the disc-like member; and an outer valve sheet attached to the outer side surface of the disc-like member and having discharge reed valve elements formed integrally therein, each of which is arranged so as to open and close the corresponding discharge port of the disc-like member. Each of the front and rear valve plate assemblies is also provided with suction openings aligned with passages formed in the front or rear cylinder block, respectively, whereby the suction chambers formed by the front and rear housings are in communication with the swash plate chamber into which a fluid or refrigerant is introduced from an evaporator of an air-conditioning system, through a suitable inlet port formed in the combined cylinder blocks.
In the swash plate type compressor as mentioned above, for example, the shaft member is driven by the engine of an automobile through a magnetic clutch, so that the swash plate member is rotated within the swash plate chamber, and the rotational movement of the swash plate member causes the double-headed pistons to be reciprocated in the pairs of aligned cylinder bores. When each piston is reciprocated in the aligned cylinder bores, a suction stroke is executed in one of the aligned cylinder bores and a compression stroke is executed in the other cylinder bore. During the suction stroke, the suction reed valve element is opened and the discharge reed valve element is closed, whereby the refrigerant is delivered from the suction chamber to the cylinder bore through the suction port. During the compression stroke, the suction reed valve element concerned is closed and the discharge reed valve element concerned is opened, whereby the delivered refrigerant is compressed and discharged from the cylinder bore into the discharge chamber, through the discharge reed valve element.
In the compressor as mentioned above, as soon as the magnetic clutch is engaged to operationally connect the compressor to the engine of an automobile, the compressor is run at full capacity so that the engine is suddenly subjected to a large load from the compressor. Accordingly, a driver of the automobile has an uncomfortable feeling when the engine bears the sudden large load. Also, the magnetic clutch is subjected to damage due to the sudden large load, and thus it is prematurely deteriorated. Furthermore, when a part of the refrigerant remains as a liquid phase in the cylinder bores, not only can a noise be generated at an initial running of the compressor, but also the pistons and the valve elements may be subjected to damage.
Japanese Unexamined Patent Publication (Kokai) No. 59(1984)-115480 discloses a swash plate type compressor which is constructed such that the engine of an automobile can be prevented from being subjected to a sudden large load when engaging a magnetic clutch for operationally connecting the compressor to the engine. In particular, a bypass passage is formed in the cylinder block for communicating the cylinder bore with the suction chamber, and a spool valve is incorporated into the bypass passage to be moved by a differential pressure between the suction chamber and the discharge chamber. At an initial running of the compressor, the spool valve is resiliently biased to an open position so that a part of the compressed refrigerant is returned to the suction chamber through the bypass passage, and the remaining part thereof is discharged into the discharge chamber through the discharge reed valve. As the pressure of the discharge chamber becomes higher, the spool valve is moved from the open position toward a closed position due to a differential pressure established between the discharge and suction chambers. As soon as the bypass passage is closed by the spool valve, the compressor is run at full capacity. Accordingly, the engine of an automobile can be prevented from being subjected to a large load at the initial running of the compressor. Nevertheless, the compressor cannot be smoothly coupled to the engine because the bypass passage is suddenly closed by the spool valve. Accordingly, a driver of the automobile may have an uncomfortable feeling when closing the bypass passage, and the magnetic clutch may be subjected to damage due to the sudden closing of the bypass passage.